1. Field of the Invention
The present invention relates generally to molecular biology and biochemistry and more specifically to a protein kinase, IκB kinase, which is activated in response to environmental stresses and proinflammatory signals to phosphorylate inhibitors of the NF-κB transcription factors and to methods of using the protein kinase.
2. Background Information
The induction of gene expression due to exposure of a cell to a specific stimulus is a tightly controlled process. Depending on the inducing stimulus, it can be critical to survival of the cell that one or more genes be rapidly induced, such that the expressed gene product can mediate its effect. For example, an inflammatory response stimulated due to an injury to or infection of a tissue results in rapid vasodilation in the area of the injury and infiltration of effector cells such as macrophages. Vasodilation occurs within minutes of the response and is due, in part, to the expression of cytokines in the injured region.
The rapid induction, for example, of an inflammatory response or an immune response, requires that the transcription factors involved in regulating such responses be present in the cell in a form that is amenable to rapid activation. Thus, upon exposure to an inducing stimulus, the response can occur quickly. If, on the other hand, such transcription factors were not already present in a cell in an inactive state, the factors first would have to be synthesized upon exposure to an inducing stimulus, greatly reducing the speed with which a response such as an inflammatory response could occur.
Regulation of the activity of transcription factors involved in such rapid induction of gene expression can occur by various mechanisms. For example, in some cases, a transcription factor that exists in an inactive state in a cell can be activated by a post-translational modification such as phosphorylation on one or more serine, threonine or tyrosine residues. In addition, a transcription factor can be inactive due to an association with a regulatory factor, which, upon exposure to an inducing stimulus, is released from the transcription factor, thereby activating the transcription factor. Alternatively, an inactive transcription factor may have to associate with a second protein in order to have transcriptional activity.
Rarely, as in the case of glucocorticoids, the inducing stimulus interacts directly with the inactive transcription factor, rendering it active and resulting in the induction of gene expression. More often, however, an inducing stimulus initiates the induced response by interacting with a specific receptor present on the cell membrane or by entering the cell and interacting with an intracellular protein. Furthermore, the signal generally is transmitted along a pathway, for example, from the cell membrane to the nucleus, due to a series of interactions of proteins. Such signal transduction pathways allow for the rapid transmission of an extracellular inducing stimulus such that the appropriate gene expression is rapidly induced.
Although the existence of signal transduction pathways has long been recognized and many of the cellular factors involved in such pathways have been described, the pathways responsible for the expression of many critical responses, including the inflammatory response and immune response, have not been completely defined. For example, it is recognized that various inducing stimuli such as bacteria or viruses activate common arms of the immune and inflammatory responses. However, differences in the gene products expressed also are observed, indicating that these stimuli share certain signal transduction pathways but also induce other pathways unique to the inducing stimulus. Furthermore, since inducing agents such as bacteria or viruses initially stimulate different signal transduction pathways, yet induce the expression of common genes, some signal transduction pathways must converge at a point such that the different pathways activate common transcription factors.
A clearer understanding of the proteins involved in such pathways can allow a description, for example, of the mechanism of action of a drug that is known to interfere with the expression of genes regulated by a particular pathway, but the target of which is not known. In addition, the understanding of such pathways can allow the identification of a defect in the pathway that is associated with a disease such as cancer. For example, the altered expression of cell adhesion molecules is associated with the ability of a cancer cell to metastasize. However, the critical proteins involved in the signal transduction pathway leading to expression of cell adhesion molecules have not been identified. Thus, a need exists to identify the proteins involved in signal transduction pathways, particularly those proteins present at the convergence point of different initial pathways that result in the induction, for example, of gene products involved in the inflammatory and immune responses The present invention satisfies this need and provides related advantages as well.